Telephone-exchange system



4 Feb. 36; 1924.

A. E. LUNDELL TELEPHONE EXCHANGI; SYSTEM Filed Apiil 28 1920 4 Sheets-Sheet l v //4 van 20/ f/ban A M/MW/ A. E. LUNDELL TELEPHONE EXCHANGE SYSTEM Feb. 26 1924.

FiI Led April 28, 15320 4 Sheets-Sheet z [IHI- i Q E dH JUU) FebQZfi 1924.

A. E. LUNDELL TELEPHONE EXCHANGE YSTEM Filed April 28, 1920 4 Sheets-Sheet 5 //7 Q/H far Alba/4 f. L uHa H/ A. E. LUNDELL TELEPHdNE EXCHANGE SYSTEM Fil'ed April 28 1920 4 Sheets-Sheet 4' wt m van/0r fi/bew f L Lmae/A Patented Feb. 26, 1924.

ALBEN' E. LUNDELL, OF CHICAGO, ILLINOIS,

PANY, INCORPORATED, OF NEW YORK, N.

ASSIGNOR T0 WESTERN ELECTRIC COM- Y., A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Application filed April 28, 1520. Serial No. 377,358.

To all whom it may concern:

Be it known that 1, Annex E. LUNDELL, a citizen of the United States, residing at Chicago, in theeounty of Cook, State of Illinois, have invented certain new and useful Improvements in Telephone-Exchange Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to telephone exchange systems and more particularly to circuits and apparatus for extending connections from an automatic exchange to manual exchanges of the magneto type.

In small rural communities, exchanges of the magneto type are quite frequently employed. Lines of such exchanges are equipped with magneto generators at the substations and with drop signals at the central exchange by means of which the subscribers may signal the operator to initiate a call. The operators cord circuits of such exchanges are also provided with supervisory drop signals which may be operated by a subscriber after a cord circuit has been connected with his line for the purpose of giving the operator a disconnect signal. When it is desired to establish aconnection between a subscriber in an automatic exchange and a subscriber in such a magneto exchange over a trunk line extending between the exchanges some provision is necessary for supplying magneto current to the trunk line for the purpose of operating the drop signals at the magneto exchange, since the automatic exchange is of the common battery type and therefore the current supplied to lines or trunks to which the selector switches of such exchange have access is not of such character as will operate the drop signals.

The principal object of this invention is to overcome this difficulty by providing means associated with the interofiice trunk extending between an automatic exchange and a magneto exchange, for operatlng the signahng devices at the magneto exchange both upon seizure and release of'the trunlr circuits. 7

A feature of the invention'resides' in the provision ofmeans associated with an interoflice trunk extending between an automatic and a magneto exchange comprising a group of relays and a source of alternating current for causing the application of the alternating current to the incoming en of the trunk circuit as soon as the outgoing end of the trunk circuit is seized, and again upon release of the outgoing end of the trunk circuit, for operating dro signals associated with the incoming end of the trunk circuit and with the cord circuit at the magneto exchange.

A further feature of the invention resides in the provision of a double wound quick acting relay and a slow acting relay with their windings and contacts so interrelated that the quick acting relay retains its armatures attracted for an appreciable time even upon a momentary initial impulse through one of its windings, for the purpose of maintaining the connection of the source of alternating current to the incoming end of the interoflice trunk for a period sufiicient to insure the operation of the drop signals at the magneto exchange.

Other features of the invention will be apparent as the description of the improved system progresses. The invention will now be described in connection with one specific embodiment of the genus of the invention.

In the accompanying drawings,-

Fig. 1 illustrates a calling subscribers line. an operators connecting circuit, and a group switch which has access to trunk circuits extending to other selector switches in the automatic exchange, and to interofiice trunk circuits extending to an outlying megneto exchange;

Fig. 2 shows a final selector switch having access to subscribers lines in the automatic exchange, and one .subscribers line to which such selector has access;

Fig. 3 shows an operators controlling apparatus by means of which the selector switches may be set; and

Fig. 4: shows an interofiice trunk circuit terminating in a jack before an operators position in a magneto exchange, a cord circuit in such an exchange, and a subscribers line, together with such circuits and equipment associated with the trunk circuit as is necessary to operate the drop signals at the magneto exchange.

Fig. 2, when placed to the right of Fig. 1,

' being well known in the art. A complete description of the operation of such switches may be found in Patent No. 1,168,319, issued January 18, 1916 to A. E. Lun dell.

It is thought a clearer understanding of the invention will be had from a detailed description of the establishment of connections between subscribers. It will first be assumed that the calling subscriber at station 100 desires to obtain a connection with the subscriber at station 200 in his own exchange.

Extension 07 connection between subscribers in the automatic exchange.

Assuming that the calling subscriber at station 100, desires to obtain a connection with a subscriber at station 200, he will remove his receiver from the switchhook, and close thus a circuit for the line relay LR which lights a calling signal CL. The operator noticing that the lamp CL is lighted, inserts a plug 101 of an idle link circuit at her position into a jack 102 in which the calling line terminates, whereupon a circuit is closed from grounded battery through the winding of cut-oif relay CO, sleeve contacts of jack 102 and plug 101, and the winding of relay 103 to ground. Relay 103 closes a circuit from grounded battery, through the power magnet of sequence switch 105, through the sequence switch contact 104, thence to ground at the armature and front contact of relay 103. Under the control of a master spring 106, sequence switch 105 moves out of position 1 and into position 2. A circuit is now closed from ground, through sequence switch contact 107, conductor 108 and contact 300 of sequence switch 301 and the winding of relay 302 to grounded battery. Relay 302 becomes energized and closes a circuit from ground, through its left-hand armature and front contact, the contact 303 and the power magnet of sequence switch 301 to grounded battery. Under the control of the master spring 3045, se quence switch 301 is moved out of position 1 and into position 3. Relay 302 does not become deenergized when sequence switch 301 leaves position 1, a circuit being closed from grounded battery, through the winding of this relay, sequence switch contact 305, the right hand armature and frontconrality of digits in order tact of relay 302, conductor 306 and contact 109 of sequence switch 105 to ground.

The operator, by depressing her listening key 110 connects her telephone set 111 into telephonic association with the calling subscribers line and in accordance with instructions received from the subscriber, she adjusts her controlling apparatus. Only two rows of keys are shown in Fig. 3, as it is thought sufficient for the purpose of the present invention to describe the setting of an interconnecting means such as a selector switch 112 and a connecting means such as a selectively operable connector switch 201, each in accordance with one digit of the called subscribers number. It will be obvious to those skilled in the art that both switches will-be set in accordance with a plu-' to extend the calling line toward the called line, and for this purpose a plurality of rows of keys must be provided at the operators position. Supposing, however, that the called subscribers line may be seized by causing selector switch 112 to take three steps and connector switch 201 to take ten steps, the operator will depress keys 310 and 311 and a start key 312. A circuit is established from ground, through the contact of key 312, the contact 313 and the power magnet of sequence switch 301 to grounded battery for moving this sequence switch into position 4. A circuit is then closed from grounded battery, through the winding of relay 113, sequence switch contact 11 1, conductor 115, sequence switch contact 314, the outer armature and back contact of the upper counting relay 0, the winding of a stepping relay 315, conductor 316, and thence to ground at sequence switch contact 116. Relays 113 and 315 become energized in this circuit, relay 113 closing a circuit from ground, through its right-hand armature and front contact, sequence switch contact 117, conductor 118, the power magnet of sequence switch 105 to grounded battery for moving this sequence switch into position 3. Relay 113 remains energized upon the opening of contact 114 due to the closure of a substitute path through the lefthand armature and front contact of this relay and sequence switch contact 119.

Upon the energization of stepping relay 315, a circuit is closed from ground,through grounded battery. The upper counting relay 2, however, cannot become energized due to the presence of the short circuit around its winding, to ground through the armature and front contact of stepping relay 315.

In position 3 of sequence switch 105, a circuit is closed from grounded battery, through the winding of the up-drive magnet 120 of the group selector switch, through sequence switch contact 121 and thence to ground, through the front contact and righthand armature of relay 113. Magnet. 120 attracts its armature 122 and presses the depending portion 123 of the switch shaft against the constantly rotating up-drive roller 174. The switch shaft with the brushes 124, 125 and 126 and commutator wipers 127 and 128 is thereby moved in an upward direction, the brushes 124, 125 and 126 wiping over the terminal bank 129 and the commutator wipers 127 and 128 over conducting and insulated segments of a commutator plate 130. When the commutator wiper 128 engages a conducting segment 131, it connects ground through this segment and conductor 132, sequence switch contacts 133 and 119, through the winding of relay 113 to grounded battery, thus shunting out the stepping relay 315. Relay 315 opensat its front contact and armature, the short-circuit of the upper counting relay 2, whereupon this counting relay becomes energized and connects conductor 322 through its armature and front contact, and armature and back contact of the upper counting relay 1, the winding of the lower counting relay 1 and conductor 323 to grounded battery. The lower counting relay 1, however, cannot become energized until commutator wiper 128 is moved into engagement with an insulating segment 134 of the commutator plate, thereby permitting the reenergization of relay 315 which again connects ground to the conductor 322.

The operation of the counting relays continues in substantially the same manner until the shaft of selector 112 has been moved upwardly three steps and the upper counting relay 0 has become energized. This counting relay, upon energizing, opens at its outer armature and back contact, the fundamental circuit including relays 113 and 315 and closes, at its inner armature and front contact, a circuit extending from ground at sequence switch contact 324, through the magnet winding of sequence switch 301 for driving the sequence switch out of position 4 and into position 6. When the sequence switch leaves position 4, all

. the counting relays which have been locked up over conductor 321 become deenergized. Relay 113, upon deenergizing, closes a circuit from ground, through its right-hand armature and back contact, sequence switch contact 135, conductor 118, and the power magnet of sequence switch 105 to grounded battery for moving this sequence switch out of position 3 and into position 6. When sequence switch 105 leaves position 3, the up-drive magnet 120 becomes deenergized.

A circuit is now closed from ground, through sequence switch contacts 136 and 137 and the right-hand winding of test relay 138 to grounded battery. Assuming that the trunk line 202, 203, and 204, terminating in the first contact set of the third group of contacts of terminal bank 129 is the first to be engaged and is idle, that is to say,- no busy ground potential is connected to test contact 139 and the multiples thereof, then when the brushes of the selector engage this set of bank terminals, the selector switch need not be moved farther. When the trunk is idle, sequence switch 205, associated with selector 201, is in position 1, thus the trunk holding relay 206 is deenergized.

VVhenthe relay 138 is energized, a circuit was closed from the ground, through its right-hand armature and front contact, sequence switch contact 140, conductor 118 and through the power magnet of sequence switch 105 to grounded battery, for driving the sequence switch out of position 6 and into position 7. Upon leaving position 6, the sequence switch opens the initial energizing circuit of relay 138 at contact 136 and if the trunk terminals which the brushes of the selector then engage are busy, the relay 138 will be maintained energized in positions 6 and 7 of the sequence switch for causing the movement of selector 112 to the terminals of another trunk. As soon as the brushes engage the brushes of an idle trunk, this maintaining circuit for relay 138 is opened and as soon thereafter as the commutator wiper 127 engages an insulated segment 141 of the commutator 130, relay 138 becomes deenergized and opens the circuit which extended through sequence switch contact 145 and the magnet winding of the up-drive magnet 120, at its right-hand armature and front contact, thereupon causing the brushes to be brought to rest on the terminals of an idle trunk. Relay 138 at its right-hand armature and back contact closes a circuit from ground, through sequence switch contact 146, conductor 118, and the power magnet of sequence switch 105 for driving this sequence switch out of position 7 and into position 11.

Sequence switch 301 is now in position 6, sequence switch 105 in position 11, and sequence switch 205 in position 1 and all of the counting relays employed in the operation of the group selector are now deenergized.

The fundamental circuit therefor will be again closed but now from grounded battery,

through the winding of relay 207 sequence switch contact 208, trunk conductor 202, brush 124 of selector 112, sequence switch contact 150, conductor 115, sequence switch contact 314, the outer armature and back contact of the upper counting relay 0, the winding of stepping relay 315, conductor 316, sequence switch contact 151, wiper 125 of selector 112, trunk conductor 203, and sequence switch contact 209 to ground. Helay 207 energizes in this circuit and closes, at its right-hand armature and front contact, a circuit extending through sequence switch contact 210, and through the magnet winding of sequence switch 205 to grounded battery for driving this sequence switch out of position 1 and into position 2. Upon leaving position 1, sequence switch 205 opens the initial energizing circuit of relay 207 but this relay is maintained energized over a locking circuit extending through its winding, its left-hand armature and front contact, through sequence switch contact 211, and thence over the circuit previously traced.

In position 2 of sequence switch 205, a circuit is closed from ground, through sequence switch contact 212, and the winding of relay 206 to grounded battery. This relay locks itself up from grounded battery, through its winding, its left-hand armature and front contact, test conductor 204 of the selected trunk circuit, selector brush 126, conductor 152, the inner left-hand armature and back contact of rela 138, and thence to ground. Relay 206 and at its right-hand armature and front contact closes a circuit extending through sequence switch contact 213 and through the magnet winding of sequence switch 205 to grounded battery, for driving this sequence switch out of position 2 and into position 3. In position 3 of sequence switch 205 a circuit is established for the rip-drive magnet 215 of the final selector switch 201, which circuit extends from grounded battery, through the magnet winding 215, sequence contact 216 and thence to ground at the right-hand armature and front contact of relay 207. Magnet 215, by attracting its armature 217, presses the depending portion of the brush shaft 218 against the constantly rotating up-drive roller 219, whereby the switch shaft and the brushes 220, 221, and 222 and commutator wiper 223 are caused to move in an upward direction. The brushes 220 and 221, in which the trunk conductors 202 and 203 terminate, and the test brush 222 are adapted to'wipe over a contact bank 224, in which called lines terminate and the commutator wiper 223 over conducting and insulated segments 225 and 226 of a commutator plate 227.

Stepping relay 315 was energized over the fundamental circuit in series with relay 207,

and upon energization closed a circuit from ground, through its front contact and arma t-ure sequence switch contact 330, conductor 331 and the contact of key 311, conductor 332, armature and back contact of upper counting relay 9, and the winding of the lower counting relay 9 to grounded battery. The counting relays operate in the same manner as above described, under the control of stepping relay 315.

The upward movement of the switch shaft of the final selector causes the commutator wiper 223 totraverse over the conducting and insulated segments 225 and 226 of the commutator plate 227, thereby intermittent ly connecting a shunt circuit around the winding of the stepping relay 315, which shunt circuit may be traced from ground at the commutator wiper 223, through the conducting segments 225 conductor 230, to sequence switch contact 231. After the switch shaft has been moved upwardly ten steps, the upper counting relay 0 will, in the well-known manner, become energized, opening at its outer left-hand armature and back contact, the fundamental circuit extending through the windings of relays 315 and 207, whereupon these relays become deenergized. The upper counting relay 0 also closes a circuit from ground, through sequence switch contact 324, the inner armature and front contact of the upper counting relay 0, and power magnet of sequence switch 301, to grounded battery for driving the sequence switch out of position 6 and into position 16, whereupon a circuit is closed from ground, through sequence switch contact 335, conductor 336, contact 155 of sequence switch 105 and power magnet of sequence switch 105' to grounded battery, and this sequence switch is moved out of position 11 and into position 16. Upon the opening of contact 109 of sequence switch 105 when the sequence switch moves out of position 11, relay 302 becomes deenerg'ized and closes a circuit from ground, through its left-hand armature and back contact, sequence switch contact 337 and the power magnet of sequence switch 301 to grounded battery for moving this sequence switch out of position 16 and into position 1;

Upon the deenergization of relay 207, when the upper O counting relay opened the fundamental circuit, the circuit of the up-drive magnet 215 is opened atthe righthand armature and front contact of relay After the testing of this line in the well-known manner. through the sequence switch contact 233, a ringing circuit is closed from a ringing current source 234, through the winding of relay 235, sequence switch contact 236, brush 221, the line loop of the desired subscribers line, brush 220 and sequence switch contact 237 to ground. Upon the removal of the receiver at the called substation, marginal relay 235 becomes energized and closes a .circuit from ground, through sequence switch contact 238, the front contact and armature of relay 235, and the power magnet of sequence switch 205 to grounded battery for driving this sequence switch out of position 13 and into the talking position 16. When sequence switch 205 leaves position 13, relay 235 becomes deenergized. The calling and called subscribers are now connected in a telephonic circuit indicated in heavy lines in the drawings.

Upon the establishment of the talking circuit to the line of the desired subscriber, the calling supervisory relay 246 becomes energized in a circuit extending from grounded battery, through the lower righthand winding of repeating coil 247, the winding of supervisory relay 246, brush 221, over the subscribers line loop back through brush 220, sequence switch contact 253, and to ground through the upper right-hand winding of repeating coil 247. Relay 246 energizes in this circuit and at its armature and front contact closes a circuit for the reversing relay 248, which circuit may be traced from grounded battery, through the winding of this relay, and thence to ground at the armature contacts of relay 246. Relay 248 by attracting its armatures reverses the connections between the terminals of the battery 249 and the conductors 202 and 203 of the trunk circuit, thereby causing the operation of the polarized supervisory relay 161 at the operators position in such a manner as to indicate to the operator that the desired subscriber has responded.

The subscribers, desiring disconnection, restore their receivers to their respective switchhooks. The restoration of the calling subscribers receiver causes the deenergiza tion of the answering supervisory relay 160 at the operators position to light the supervisory lamp in the well-known manner. The restoration of the receiver at the called subscribers substation, causes the deenergization of supervisory relay 246 and the consequent deenergization of relay 248 which thereupon reverses the connection of the terminals of battery 249 to the trunk conductors 202 and 203 for, causing the reverse operation of the polarizedsupervisory relay 161 to thereby light the calling supervisory lamp at the operators position. The operator noticing these signals, removes the plug 101 from the jack 102,

whereupon relays CO and 103 become deenergized, the former restoring the connection of the windings of the line relay LE to the limbs of the calling subscribers line, and the relay 103 closing a circuit from ground, through its armature and back contact and the contact 162 of the sequence switch, and thence to the power magnet of sequence switch 105 to grounded battery for driving the sequence switch out of position 16 and into position 18.

In position 18, a circuit is closed from grounded battery, through the winding of the down-drive magnet 163, which circuit may be traced from the winding of this magnet, through sequence switch contact 164, to ground. Magnet 163 presses the depending portion of the switch shaft 123 against the constantly rotating down-drive roller 166, whereby the switch shaft is moved downwardly into its normal position. When the shaft reaches its normal position, a circuit is closed from ground, through commutator wiper 127, normal segment 167, conductor 168 sequence switch contact 169, conductor 118, andthence to grounded battery through the power magnet of sequence switch 105 for driving this sequence switch out of position 18 and into position 1. WVhen the sequence switch leaves position 18, the downdrive magnet 163 becomes deenergized.

As soon as the brush 126 of the group selector leaves the terminal of the trunk conductor 204, the locking circuit of relay 206 is opened and this relay becomes deen'ergized. At its left-hand armature and back contact, the relay connects the test conductor 204 to ground at sequence switch contact 240 to prevent the seizure of the trunk circuit by other group selectors until the final selector is completely restored to normal and, at its right-hand armature and back contact, closes a circuit extending through sequence switch contact 241 for driving the sequence switch 205 out of position 16 and into position 18.

In position 18, a circuit is closed extending from ground at sequence switch contact 242, through the winding of the downdrive magnet 243 for causing the restoration of the switch shaft of the final selector. The energization of magnet 243 presses the depending portion 218 of the switch shaft against the constantly rotating down-drive roller 254 which moves the switch shaft downwardly into normal position. Upon reaching its normal position, the commutator wiper 223 closes a circuit extending from ground, through this wiper, the normal segment 224 of the commuator, conductor 245, sequence switch contact 246, and through the magnet winding of sequence switch 205 for driving the sequence switch out of position 18 and into position 1. In

position 1 of sequence switch 205, the trunk 202 203 and 204. mav be a ain seized 1n the above-described manner.

Establishment of a; connection to a magneto exchange.

It will now be assumed that the calling subscriber desires to establish a connection with a subscriber whose substation is No. 450 located in an outlying exchange which is of the magneto type. Upon the initiation of the call, the operator extends a connection through the plug 101 to the calling subscribers line in the manner previously described, and the fundamental circuit extending through the relay 113 in position 3 of sequence switch 105, and through the stepping relay 315 in position 4 of sequence switch 301 is established in the manner previously described. The operator, in response to the instructions of the calling subscriber, depresses the key 340 in the first row of digit keys and the start key 312. Whenever key 340 is de pressed the selector switch 112 is controlled to direct the connection directly to a mag neto office and since no final selector is employed on such connections, the key is provided with an additional contact for advancing the sender sequence switch to position 16, thus preventing the sender from exercising further control over the connection. The group selector is now driven in the manner previously described under the control of the counting relays to position its brushes in association with the fourth group of trunks terminating in its bank 129.

When the switch shaft has been so positioned, the upper counting relay 0 energizes, opening at its outer left-hand armature and back contact the fundamental circuit extending through the relay 113 and the stepping relay 315, and at its inner left-hand armature and front contact closes a circuit extending through sequence switch contact 324 for driving sequence switch 301 out of position 4. Upon leaving position 4, the locking circuit for the bank of counting relays is opened at sequence switch contact 320 but, since the operator has depressed key 340 corresponding to the group of trunks extending to the desired magneto exchange, a new circuit is established for the lower counting relay 0 as soon as sequence switch 301 reaches position 5, this circuit extending from grounded battery, through the winding of the lower counting relay 0, through the conductor 341, sequence switch contact 342, and thence to ground at the right-hand contacts of key 340. This circuit is maintained at sequence switch contact 342 through position 59;. 'When the lower counting relay 0 energizes, a locking circuit is closed through the winding of the lower counting relay 0 relay 403. Relay which may be traced from grounded battery, through the winding of this relay, through the winding of the upper counting relay 0, and thence to ground at sequence switch contact 320. The upper counting relay 0 energizes in this locking circuit as soon as the shunt around its winding is removed at sequence switch contact 342, when the sequence switch leaves position 5 The energization of the upper counting relay 0 closes a circuit at its inner armature and front contact for driving sequence switch 301 out of position 6 and into position 16. I

Following the operation of the selector switch in accordance with the first digit of the number when relay 113 became energized, sequence switch 105 was driven out of position 3 and into position 6 as previously described, and the selector switch is thereupon caused to hunt for an idle trunk circuit in the group to which its brushes have selectively moved, and upon the selec tion of an idle trunk circuit, the. sequence switch 105 is driven into position 11 in the manner previously described. Since now the sequence'switch 301 is in position 16, a circuit is established from ground at sequence switch contact 335, extending over conductor 336 and through sequence switch contact 155, for driving the sequence switch 105 out of position 11 and into position 16.

A circuit is now established over the, selected trunk conductors 250 and 251 for the trunk relay 400 associated with the'incoming end of the selected interotfice trunk. The circuit for this relay extends from grounded battery, through its right-hand winding, the back contact and upper armature of cutoff relay 401, over trunk conductor 250, selector brush 124, sequence switch contact 170, through the winding of polarized supervisory relay 161, sequence switch contact 171, selector brush 125, trunk conductor 251, intermediate armature and back contact of relay 401, and thence to ground through the left-hand winding of relay 400. Relay 400 energizes in this circuit and, at its left-hand armature and front contact, closes a circuit through the winding of slow releasing relay 402, and also a circuit in parallel with the winding of relay 402, extending through the lower winding of ringing 402, upon energizing, closes at its right-hand armature and front contact, a circuit extending through the upper winding of relay 403, and at its lefthand armature and front contact, closes a circuit extending from ground at the righthand armature and front contact of relay 400, through the left-hand armature and front contact of relay 402, and thence to grounded battery, through the winding of the trunk holding relay 404. Relay 404 energizes in this circuit and at its upper armature and front contact, closes a locking circuit for itself extending over the test conductor 252 of the interoffice trunk circuit, through the brush 126 of the group selector, conductor 152, inner left-hand armature and back contact of test relay 138, and thence to ground.

Ringing relay 403, upon energizing, connects the source of ringing current 405 to the incoming end of the trunk circuit for operating the drop signal 406, this circuit extending from a source of ringing current 405, through the front contact and itnermediate armature of relay 403, through the ring jack contact 407, the winding of drop signal 406, the tip jack contact 408, and thence to ground at the upper armatureand front contact of ringing relay 403. Current from the source of ringing current 405 causes the operation of the drop signal to signal the operator at the magneto exchange oflice that a call is incoming over the interoifice trunk with which the drop signal is associated.

At the time relay 404 energized, a circuit was closed for relay 401 extending from grounded battery, through the winding of this relay, through the lower armature and front contact of relay 404, and thence to ground at the front contact and lowermost armature of ringing relay 403. Relay 401, upon energizing, opens at its upper and intermediate armatures and back contacts, the circuit extending through the windings of trunk relay 400, and at these armatures and their front contacts, extends the talking conductors of the trunk circuit to the back contacts of the upper and intermediate armatures of ringing relay 403. Relay 400, upon becoming disconnected from the interottice trunk circuit, immediately deenergizes, opening the initial energizing circuit extending through the lower winding of ringing relay 403 and the circuit extending in parallel therewith, through the slow release relay 402. The slow release relay 402 deenergizes after an interval, opening at its right-hand armature and front contact, the circuit extending through the upper wind-- ing of relay 403, and the ringing relay 403 thereupon deenergizes to disconnect the source of ringing current 405 from the winding of the drop signal 406. At its lowermost armature and front contact, relay 401 closes a locking circuit for itself which extends to ground at the right-hand armature and back contact of relay 402 as soon as relay 402 deenergizes. A second locking circuit is also closed for relay 401 through the back contact and lowermost armature of ringing relay 403.

The operator at the magneto exchange, upon noting the operation of the drop signal 406, selects an idle cord circuit at her position and inserts the answering plug 409 thereof in the jack of the trunk circuit which has been seized for the use of the calling subscriber at the automatic exchange, thereby cutting ofi' the drop signal 406 at the jack springs, and depresses her listening key 410 to connect her telephone set 411 to the cord circuit. The operator then receives instructions from the calling subscriber as to the number of the line. desired in the magneto exchange and, in accordance with such instructions, inserts the calling plug 412 of th cord circuit in the jack 413 of the desired line. She then proceeds to call the subscriber on the desired line by applying ringing current from the source 414, through the contacts of ringing key 415. Upon the response of the called subscriber, the subscribers are connected into a talking circuit extending over the heavy conductors. The calling subscriber receives talking current from the battery in the cord circuit at the automatic exchange and the called subscriber is provided with talking current from a source local to his substation.

Upon the termination of the conversation, the calling subscriber restores his receiver to its switchhook, thereby opening the circuit extending through the supervisory relay 160 which upon deenergization causes the operation of the usual supervisory signal. The operator, in response to this signal, removes the plug 101 from the jack 102, caus ing thereby the deenergization of relay 103 which, at its armature and back contact, closes a circuit for driving sequence switch 105 into position 18. In position 18, the selector switch is restored to normal position in the manner previously described and, upon reaching normal position, closes a circuit for driving sequence switch 105 out of position 18 and into position 1.

Upon the restoration of the switch shaft of selector 112 and the removal of the switch brushes from the terminals of the interofiice trunk, the holding circuit of relay 404 is opened and this relay thereupon becomes deenergized, closing at its lower armature and back contact, a circuit for the ringing relay 403 which extends from grounded battery, through the lower winding of this relay, through the left-hand armature and back contact of trunk relay 400, the back contact and lower armature of relay 404, the lowermost armature and front contact of relay 401, and thence to ground at the back contact and lowermost armature of relay 403. Relay 402 is also energized in parallel with the lowermost winding of relay 403, closing at its right-hand armature and front contact, a circuit extending through the upper winding of relay 403. Relay 403, upon energizing, again connects the source of ringing current 405 to the incoming ends of the interoflice trunk circuit and since now the plug 409 is in the jack of the trunk circuit, the ringring current is connected to the winding of I the clearing-out drop signal 416 associated with the operators cord circuit. The energization of relays 402 and 403 has opened the locking circuit of relay 401 which now deenergizes, opening at its lowermost armature and front contact, the initial energizing circuit for relays 402 and 403, which relays, after an interval, deenergize, the relay 403 thereby disconnecting the source of ringing current 405 from the trunk circuit.

The operator at the magneto exchange, upon noting the operation of the clearingout signal 416 pulls down the cord circuit from the jack of the interoffice trunk and from the jack of the called line. The circuits which were employed in extending a connec tion from the calling subscribers line 100 in the automatic exchange to the called subscribers line 450 in the magneto exchange are now completely restored to normal condition.

It is apparent from the foregoing description that the seizure of an interoifice trunk by a group selector in the automatic ex change automatically effects the application of a source of ringing current to the incoming end of the interoffice trunk for operating a drop signal, and without the employ ment of any source of current at the group selector of the automatic exchange. The circuits associated with the incoming end of the interoffice trunk are also effective for con necting the source of ringing current to the cord circuit at the magneto exchange for automatically producing a disconnect signal upon the release of the interoflice trunk circuit at the outgoing end thereof. It is further apparent that the relation of the winding of the slow relay 402 and the armature contacts of such relay, with the windings of the double wound ringing relay 403, is such that upon a momentary impulse of current through one winding of relay 403, the relay 403 is caused to maintain its energization for an appreciable period after the cessation of such impulse of current. This feature is particularly important in that it enables the source of ringing current to be connected to the winding of the drop signals 406 and 416 for a sufficient period to insure the operation of the signals.

That is claimed is:

1. In a telephone exchange system, an originating ofiice, an outlying office, trunk lines extending between said offices, an automatic switch in said first office for selecting one of said trunk lines, responsive means individual to said trunk line at the outgoing end thereof, a signal associated with said trunk line at the incoming end thereof, means made effective by the seizure of said trunk line by said switch to operate said responsive means, and means under the control of said responsive means for operating said signal.

2. In a telephone exchange system, an originating oflice, an outlying office, trunk lines extending between said offices, a cord circuit at said second office for connection with said trunk lines, an automatic switch in said first office for selecting one of said trunk lines, responsive means associated with said trunk at the outgoing end thereof, a signal associated with said trunk line at the incoming end thereof, a second signal in said cord circuit, and means made effective by the seizure of said trunk line by said switch to operate said responsive means to thereby operate said first signal and effective upon release of said trunk line to operate said second signal.

3. In a telephone exchange system, an originating ofiice, an outlying office, trunk lines extending between said oflices, a cord circuit at said second office for connection with said trunk lines, an automatic switch in said first oflice for selecting one of said trunk lines, a drop signal. in said cord circuit, and means made effective by release of said trunk line at the outgoing end there of to operate said signal.

4. In a telephone exchange system, an originating office, an outlying oifice, trunk lines extending between said offices, a group selector and a final selector in said first oflice for extending connections within said first office, said group selector also being adapted to extend a connection to one of said trunk lines, a drop signal associated with said trunkline at the incoming end thereof, and means made effective by seizure of said trunk line by said group selector to operate said signal.

5. In a telephone exchange system, an originating office, an outlying office, trunk lines extending between said offices, a group selector and a final selector in said first office for extending connections within said first office, said group selector also being adapted to extend a connection to one of said trunk lines, a cord circuit at said second oflice for connection with said trunk lines, a drop signal associated with said trunk line at the incoming end thereof, a second drop signal in said cord circuit, and means made effective by seizure of said trunk line by said group selector to operate said first signal and effective upon release of said trunk line to operate said second signal.

6. In a telephone exchange system, an originating office, an outlying office, trunk lines extending between said offices, an automatic switch in said first oflice for selecting one of said trunk lines, a drop signal associated with said trunk line at the incoming end thereof, a source of alternating current for operating said signal, and means made effective by the seizure of said trunk line by said switch to connect said source in circuit with said signal.

7. In a telephone exchange system, an originating oflice, an outlying oifice, trunk lines extending between said offices, an automatic switch in said first ofiice for selecting one of said trunk lines, a drop signal associated with said trunk line at the incoming end thereof, a source of alternating current for operating said signal, a trunk relay normally connected across said trunk circuit, a double wound signaling relay for connecting said source of current with said signal, a slow releasing relay, means under the control of said trunk relay for energizing said slow relay and one winding of said signaling relay in parallel, and means under the control of said slow relay for closing a maintaining circuit for said signaling relay through the second winding of said latter relay.

8. In a telephone exchange system, the combination of a group of relays comprising a double wound relay and a slow releasing relay, one winding of said first relaybeing connected in parallel with the winding of said second relay and the other Winding of said first relay being connected into a circuit under the control of said second relay, whereby said first relay may be maintained energized for an appreciable interval after the cessation of the initial impulse of energizing current through the first-mentioned winding thereof.

9. In a telephone exchange system, a trunk line, a signaling device associated with said trunk line, a source of current for operating said device, a relay mechanism for connecting said source of current to said device comprising a double wound relay and a slow releasing relay, one winding of said first relay being connected in parallel with the winding of said second relay, and the other winding of said first relay being connected into a circuit under the control of said second relay, whereby said first relay may be maintained energized for an appreciable interval after the cessation of the initial impulse of energizing current through the firstmentioned Winding thereof.

In witness whereof, I hereunto subscribe my name this 24 day of April, A. D. 1920.

ALBEN E. LUNDELL 

